Current amplifier

Abstract

A current amplifier comprising an amplifier circuit with overall negative feedback and an output current amplification circuit. In one embodiment, a photodiode provides a current to be amplified and the amplifier circuit and the output current amplification circuit are implemented using MOS technology.

1. A current amplifier circuit comprising:
 first and second current input terminals to receive a first current;  
 an operational amplifier having a non-inverting input terminal coupled to a bias voltage and the second current input terminal, an inverting input terminal coupled to the first current input terminal, and an output terminal to provide an output of the operational amplifier;  
 a current mirror amplifier having an amplification factor, an input terminal and an output terminal and configured to provide an amplified output current that is the product of the first current and the amplification factor of the current mirror amplifier; and  
 a transistor connected between the inverting input terminal of the operational amplifier and the input terminal of the current mirror amplifier, wherein the transistor is controlled by the output of the operational amplifier.  
 
   
   
     2. The current amplifier of  claim 1 , wherein the operational amplifier is comprised of MOS transistors. 
   
   
     3. The current amplifier of claims  1 , wherein the current mirror amplifier is comprised of MOS transistors. 
   
   
     4. The current amplifier circuit of  claim 1 , wherein the current mirror amplifier comprises a Wilson current mirror. 
   
   
     5. The current amplifier of  claim 1 , wherein the transistor is an MOS transistor. 
   
   
     6. The current amplifier of  claim 1 , further comprising a photodiode coupled to the first and second current input terminals to generate the first current. 
   
   
     7. The current amplifier of  claim 1 , further comprising a CD read head coupled to the first and second current input terminals to generate the first current. 
   
   
     8. The current amplifier of  claim 7 , further comprising CD signal processing circuitry, wherein the current amplifier and the CD signal processing circuitry are integrated onto an integrated circuit. 
   
   
     9. A current amplifier comprising:
 a differential amplifier having MOS input transistors of a first conductivity type, a non-inverting input terminal coupled to a bias voltage, an inverting input terminal coupled to an input current, and an output terminal;  
 a first MOS transistor of a second conductivity type and a second MOS transistor of the first conductivity type, the first and second MOS transistors each having a control gate, wherein the control gate of the first MOS transistor is coupled to the output terminal of the differential amplifier, the first MOS transistor is connected between a first reference voltage and the control gate of the second MOS transistor, and the second MOS transistor is connected between the inverting input terminal of the differential amplifier and a second reference voltage; and  
 a current mirror amplifier having an input terminal coupled to the control gate of the second MOS transistor, and an output terminal to provide an amplified output current.  
 
   
   
     10. The current amplifier of  claim 9  wherein the current mirror amplifier comprises a Wilson current mirror. 
   
   
     11. The current amplifier of  claim 9  wherein the MOS input transistors of the differential amplifier are n-channel transistors, the first MOS transistor is a p-channel transistor, the first reference voltage is a supply voltage and the second reference voltage is a ground. 
   
   
     12. The current amplifier of  claim 9 , further comprising a photodiode to generate the input current for the differential amplifier. 
   
   
     13. The current amplifier of  claim 9 , further comprising a CD read head to generate the input current for the differential amplifier. 
   
   
     14. A current amplifier comprising:
 a first input terminal to receive a current;  
 a second input terminal to receive a bias voltage;  
 a first MOS transistor of a first conductivity type having a control gate coupled to the first input terminal;  
 a second MOS transistor of the first conductivity type having a control gate coupled to the second input terminal;  
 a constant current source having a first terminal and a second terminal, wherein the first MOS transistor is connected between the first terminal of the constant current source and a first node;  
 a third and a fourth MOS transistor of a second conductivity type and each having a control gate, wherein the second MOS transistor is connected between the first terminal of the constant current source and the control gates of the third and fourth MOS transistors, the third MOS transistor is connected between the first node and a reference voltage, and the fourth MOS transistor is connected between the control gate of the fourth MOS transistor and the reference voltage;  
 a fifth MOS transistor of the second conductivity type and having a control gate, wherein the control gate of the fifth MOS transistor is coupled to the first node;  
 a sixth MOS transistor of the first conductivity type, wherein the fifth MOS transistor is connected between the control gate of the sixth MOS transistor and the reference voltage, and the sixth MOS transistor is connected between the first input terminal and the second terminal of the constant current source; and  
 a current mirror amplifier having an input terminal coupled to the gate of the sixth MOS transistor and an output terminal.  
 
   
   
     15. The current amplifier of  claim 14 , wherein the first and second MOS transistors are n-channel MOS transistors. 
   
   
     16. The current amplifier of  claim 14 , wherein the current mirror amplifier comprises a Wilson current mirror. 
   
   
     17. A current amplifier comprising:
 first and second current input terminals to receive a first current to be amplified;  
 an operational amplifier having a low impedance inverting input terminal coupled to the first current input terminal, a non-inverting input terminal coupled to the second current input terminal, and an output terminal;  
 a feedback loop comprising a transistor, the feedback loop being connected between the output terminal and the inverting input terminal of the operational amplifier; and  
 a current mirror having an amplification factor, an input terminal to receive a current conducted through the transistor in the feedback loop and an output terminal to provide an amplified output current that is the product of the first current to be amplified and the amplification factor of the current mirror, the input terminal of the current mirror being coupled to the transistor.  
 
   
   
     18. The current amplifier of  claim 17 , wherein the operational amplifier is comprised of MOS transistors. 
   
   
     19. The current amplifier of  claim 17 , wherein the current mirror amplifier comprises a Wilson current mirror. 
   
   
     20. A current amplifier comprising:
 a current input terminal to receive a current to be amplified;  
 a voltage amplifier circuit having a first input terminal coupled to the current input terminal, a second input terminal and an output terminal;  
 a feedback loop having overall negative feedback coupled between the output terminal and the first input terminal of the voltage amplifier circuit; and  
 a current amplifier circuit coupled to the feedback loop through a continuous current path, the continuous current path conducting a current proportional to the current to be amplified, and having an output terminal providing an output current proportional to the current to be amplified.  
 
   
   
     21. The current amplifier of  claim 20  wherein the feedback loop comprises a p-channel MOS transistor. 
   
   
     22. The current amplifier of  claim 20  wherein the feedback loop comprises an n-channel MOS transistor. 
   
   
     23. The current amplifier of  claim 20  wherein the current amplifier circuit comprises a CMOS transistor. 
   
   
     24. The current amplifier of  claim 20  wherein the current amplifier circuit composes a current mirror. 
   
   
     25. The current amplifier of  claim 24  wherein the current mirror is a Wilson current mirror. 
   
   
     26. A method of amplifying a current signal, the method comprising:
 conducting the current signal between first and second inputs of an amplifier;  
 receiving a bias voltage signal at the second amplifier input;  
 providing negative feedback to the first amplifier input using a first transistor and a second transistor;  
 conducting a current of a predetermined multiple of the current of the current signal through the second transistor; and  
 generating an amplified current using an output transistor coupled to the second transistor, the amplified output current being a predetermined multiple of the current conducted through the second transistor.  
 
   
   
     27. The method of  claim 26 , wherein the step of generating an amplified current comprises mirroring in the output transistor the current flow through the second transistor. 
   
   
     28. The method of  claim 26 , comprising generating the current signal in response to data patterns detected in a compact disk by a read head. 
   
   
     29. The method of  claim 26 , further comprising integrating a signal processing circuit and a current amplifier circuit in a single integrated circuit. 
   
   
     30. A current amplifier circuit comprising:
 first and second input terminals to receive a first current to be amplified;  
 an operational amplifier having a non-inverting input terminal coupled to a reference voltage and to the second input terminal, an inverting input terminal coupled to the first input terminal and an output terminal;  
 a current input circuit coupled to the first and second input terminals;  
 a feedback circuit having a control terminal coupled to the output terminal of the operational amplifier, a first terminal coupled to the inverting input terminal of the operational amplifier and a second terminal; and  
 a current mirror circuit having its input connected to the second terminal of the feedback circuit and having an output terminal providing an output of the current amplifier circuit, wherein the feedback circuit is configured to maintain a substantially zero bias voltage across the current input circuit and the output of the current amplifier is proportional to the first current to be amplified.  
 
   
   
     31. The current amplifier circuit of  claim 30  wherein the feedback circuit includes an MOS transistor having a gate coupled to the output terminal of the operational amplifier, a first source/drain coupled to the inverting input terminal of the operational amplifier and a second source/drain coupled to the input of the current mirror circuit. 
   
   
     32. The current amplifier circuit of  claim 30  wherein the current input circuit includes a photo diode having one terminal coupled to the first input terminal. 
   
   
     33. The current amplifier circuit of  claim 32  wherein the photo diode has a second terminal coupled to the second input terminal. 
   
   
     34. A current amplifier circuit comprising:
 an operational amplifier having an inverting input terminal coupled to a reference voltage, a non-inverting input terminal and an output terminal;  
 a current input circuit coupled to the inverting and the non-inverting input terminals of the operational amplifier;  
 a negative feedback circuit having a control terminal coupled to the output terminal of the operational amplifier, a first conduction terminal coupled to the non-inverting input of the operational amplifier and a second conduction terminal; and  
 an output circuit having a control terminal coupled to the control terminal of the feedback circuit, a first terminal coupled to the second conduction terminal of the feedback circuit and an output terminal providing an output current of the current amplifier circuit proportional to a current generated by the current input circuit.  
 
   
   
     35. A method of amplifying a current signal, the method comprising:
 receiving a current signal from a photo-sensitive device;  
 conducting the current signal between a low impedance amplifier input and a second amplifier input;  
 receiving a bias voltage at the second amplifier input;  
 providing negative feedback to the low impedance amplifier input by conducting a current substantially equal to the current of the current signal through a first transistor so as to maintain a substantially zero bias voltage across the photo-sensitive device; and  
 generating an amplified current using an output transistor coupled to the first transistor, the amplified output current being a predetermined multiple of the current conducted through the first transistor.  
 
   
   
     36. A method of amplifying a current signal, the method comprising:
 receiving a current signal from a photo-sensitive device;  
 conducting the current signal between a low impedance amplifier input and a second amplifier input;  
 receiving a bias voltage at the second amplifier input;  
 providing negative feedback to the low impedance amplifier input by conducting a current substantially equal to the current of the current signal through a first transistor so as to maintain a substantially zero bias voltage across the photo-sensitive device; and  
 generating an amplified current using a current mirror coupled to the first transistor, the amplified output current being a predetermined multiple of the current conducted through the first transistor.  
 
   
   
     37. A current amplifier circuit comprising:
 first and second input terminals for coupling to a photo-sensitive device;  
 an operational amplifier having a non-inverting input terminal coupled to a bias voltage and to the first input terminal, an inverting input terminal coupled to the second input terminal, and an output terminal to provide an output of the operational amplifier;  
 a current mirror amplifier having an input terminal and an output terminal to provide an amplified output current proportional to a current conducted between the first and second input terminals; and  
 a transistor connected between the inverting input terminal of the operational amplifier and the input terminal of the current mirror amplifier, wherein the transistor is controlled by the output of the operational amplifier and the current amplifier circuit is configured to maintain a substantially zero bias voltage across the photo-sensitive device.  
 
   
   
     38. A current amplifier comprising:
 a differential amplifier having MOS input transistors of a first conductivity type, a non-inverting input terminal coupled to a bias voltage, an inverting input terminal coupled to an input current, and an output terminal;  
 a first MOS transistor of a second conductivity type and a second MOS transistor of the first conductivity type, the first and second MOS transistors each having a control gate, wherein the control gate of the first MOS transistor is coupled to the output terminal of the differential amplifier, the first MOS transistor is connected between a first reference voltage and the control gate of the second MOS transistor, and the second MOS transistor is connected between the inverting input terminal of the differential amplifier and a second reference voltage; and  
 a current mirror amplifier having an input terminal coupled to the control gate of the second MOS transistor, and an output terminal to provide an output current proportional to the input current.  
 
   
   
     39. A method of amplifying a current signal, the method comprising:
 coupling a photo-sensitive device across first and second input terminals of an operational amplifier;  
 maintaining a substantially zero bias voltage across the photo-sensitive device by applying negative feedback through a feedback loop to the first terminal of the operational amplifier; and  
 conducting a current substantially equal to current conducted through the photo-sensitive device through a first transistor of a current mirror circuit, wherein the first transistor of the current mirror circuit is coupled to the first terminal of the operational amplifier through a continuous current path.  
 
   
   
     40. The method of  claim 39 , wherein a control terminal of the first transistor is coupled to an output terminal of the operational amplifier and a current carrying terminal of the first transistor is coupled to the first terminal of the operational amplifier. 
   
   
     41. The method of  claim 39 , further comprising amplifying the current conducted through the first transistor. 
   
   
     42. The method of  claim 39 , wherein the feedback loop comprises a second transistor and a current substantially equal to the current conducted through the first transistor is conducted through the second transistor. 
   
   
     43. A current amplifier circuit comprising:
 first and second input terminals for receiving an input current from a photo-sensitive device;  
 an operational amplifier having a first input coupled to a bias voltage and the first input terminal, a second input coupled to the second input terminal, and an output to provide an output of the operational amplifier; and  
 a current mirror having an input terminal coupled through a continuous current path to the second input of the operational amplifier, a control terminal coupled to the output of the operational amplifier, and an output terminal to provide an amplified output current proportional to the input current, wherein the current amplifier circuit is configured to maintain a substantially zero bias voltage across the photo-sensitive device.  
 
   
   
     44. The current amplifier circuit of  claim 43  wherein the control terminal of the current mirror is directly connected to the output of the operational amplifier. 
   
   
     45. The current amplifier circuit of  claim 43  wherein the input terminal of the current mirror is directly connected to the second input of the operational amplifier. 
   
   
     46. The current amplifier of  claim 45  wherein the control terminal of the current mirror is directly connected to the output of the operational amplifier. 
   
   
     47. The current amplifier circuit of  claim 43 , further comprising a transistor connected between the input terminal of the current mirror and the second input of the operational amplifier, wherein a control terminal of the transistor is connected to the output of the operational amplifier and the control terminal of the current mirror is coupled to the input terminal of the current mirror. 
   
   
     48. The current amplifier circuit of  claim 43  wherein the photo-sensitive device comprises a photo-diode.